1. Field of the Invention
This invention relates in general to signal-seeking radio receivers, and in particular, to stepping radio receivers for production of audio signals from radio frequency signals, which receivers are capable of tuning to several separate channels on a plurlity of bands.
2. Description of the Prior Art
The invention disclosed and claimed herein can be considered to be an improvement on the inventions of U.S. Pat. No. 3,665,318 to Hoffman et al. and U.S. Pat. No. 3,996,521 to Owens. In prior art patents, such as the Hoffman et al. and Owens patents, band selection switch circuitry which connects to the band-selecting means precedes the RF amplifier and mixer circuitry. When a band is selected by means of a patch panel or patch board technique, and a particular channel is being scanned, a low signal biases the base of a band switch transistor turning on the transistor and causing biasing current to be supplied from a constant DC voltage source to a pair of biasing resistors which in turn condition the RF amplifier and band mixer for the particular band to be conditioned for operation.
The presence of the band switch circuitry as part of these prior art radio receivers represents additional time for fabrication of the radio receiver as well as additional costs associated with the required components. Furthermore, the greater the number of parts, the greater the chances for failure of the radio. Reduction in the amount of circuitry which manifests itself in fewer component parts and fewer connections will have the advantages of lower cost and improved reliability.
Other circuits for band selection in radio receivers are disclosed in U.S. Pat. No. 3,895,303 to Imazeki et al. and U.S. Pat. No. 3,940,697 to Morgan. However, the arrangement of Imazeki et al. is only designed for two bands and the circuitry is not usable with the multiband arrangement of Owens. The invention of Morgan employs a single mixer associated with a plurality of RF amplifier sections. The band switching in Morgan is accomplished through circuit components which either merely switch the signals on and off but do not amplify the incoming signal or require a plurality of stages which invert the polarity of the control signal.